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Sanding between coats of ployurethane

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Forum topic by BentheViking posted 1116 days ago 12115 views 0 times favorited 22 replies Add to Favorites Watch
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BentheViking

1752 posts in 1197 days


1116 days ago

Topic tags/keywords: pine spruce finishing sanding arts and crafts

I am finishing up a project that will be partly painted, and partly stained. I usually finish my projects with Minwax Polycrylic…3 coats with a light hand sanding of 320 between coats. I am really pressed for time and if I can avoid sanding between coats it would certainly be nice. That being said, I really like the look and feel of the final product the way I normally do things, so if needed I will do it that way, I guess my concern is what sort of quality dropoff can I expect if I don’t sand between coats? What about only sanding after the first? The second?

Any help will be greatly appreciated

-- It's made of wood. Real sturdy.--Chubbs Peterson


22 replies so far

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Tim Kindrick

369 posts in 1187 days


#1 posted 1116 days ago

Ditto what Cessna said!! If you want something quick and easy without sanding between coats, try using lacquer. Deft makes a brushing lacquer that works great for this because each topcoat “melts” into the one below it, so no need to sand between each coat. AND lacquer dries VERY quickly, so you can do 3 coats in one day very easily!!!

-- I have metal in my neck but wood in my blood!!

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BentheViking

1752 posts in 1197 days


#2 posted 1116 days ago

Hmmm…thats an interesting idea. What would i expect to pay for a quart of that? Where could I get it? The only time I’ve ever used laquer is a white primer with a HVLP system (which we did have to sand after we coated it, but i was impressed by its glassy smooth finish). Any tips on what to do/expect? I don’t have much time to experiment and play around so if it was much more complicated than opening the can and brushing it on I might have to pass for now.

-- It's made of wood. Real sturdy.--Chubbs Peterson

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Tim Kindrick

369 posts in 1187 days


#3 posted 1116 days ago

It’s as simple as that… open the can and brush it on. You can get it at HD or Lowes for about the same as poly or less. It comes in semi gloss or high gloss. Very easy to use if you use a good brush!!!!! According to these LJ members, you can also spray it thru an HVLP gun if you have one…. http://lumberjocks.com/topics/28939

-- I have metal in my neck but wood in my blood!!

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IrreverentJack

724 posts in 1476 days


#4 posted 1116 days ago

I just had a project with multiple coats of poly. Using a card scraper to take off any nibs or drips was very helpful before the “between coat” sanding. – Jack

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jroot

225 posts in 2155 days


#5 posted 1116 days ago

I ALWAYS sand between coats of lacuer. I don’t see using laquer as a short cut at all. It does dry quickly though… to the touch. I still do one coat a day, sand the next morning, let the dust settle, another coat is applied etc. The result is a fine finish that lasts.

-- jroot

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Tim Kindrick

369 posts in 1187 days


#6 posted 1116 days ago

jroot, yes, you can sand between coats but it’s not required like poly. Each coat of poly sits on the surface of the one below it so you have to “scuff sand” the surface before each additional coat. This also removes dust nibs that build up on poly because it dries so slowly. Lacquer doesn’t sit on the surface of the layer below it, it melts into the one below. Also, lacquer does dry to the touch very quickly but it can take days or weeks before it CURES completely. That only means you have to wait a while before “rubbing out” the finish. If you’re not planning on rubbing the finish out then it’s perfect for the situation above. As always, this is only my humble opinion!!!!!! Btw, I have applied as many as 6 coats of lacquer in one day without sanding AND without a problem!!!

-- I have metal in my neck but wood in my blood!!

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BentheViking

1752 posts in 1197 days


#7 posted 1116 days ago

thanks everyone for your quick and thoughtful responses. My wife is nagging me about spending so much time in the shop finishing my last project when she is packing our house for the move, so I’m thinking spending $10 on a new can might end up being worth far more. My schedule will still probably only allow one coat a day, but at least I won’t have to spend the time sanding.

My question is if lacquer is as easy to apply, takes less time and work between coats and costs less than polyurethane why would anyone use polyurethane? Is there some redeeming qualities?

Also since it is easiest for me to go to HD or Lowe’s it seems as if the only lacquer they carry is the Deft in satin, semi, and gloss. I would assume since Tim suggested it it has to be a halfway decent product, but is there any reason not to go with it?

-- It's made of wood. Real sturdy.--Chubbs Peterson

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Tim Kindrick

369 posts in 1187 days


#8 posted 1116 days ago

“Why would any not use lacquer?”..... Several reasons, 1. Brushing Lacquer is relatively new. Before brushing lacquer came out, all lacquer was “spray on only” and most people didn’t have spray guns or know how to use them. 2. Lacquer hasn’t always been the most durable of finishes. In the past,(I think) it was affected by alcohol and other chemicals but like I said, that was “the past”. It’s formulated to be much more durable today. 3. When it comes to “fine woodworking” lacquer is still often the prefered finish for a lot of professionals. 4. Again, (It think) poly cures a little faster and maybe, a little harder than lacquer. “Dries” and “cures” are two seperate things. If you’re not planniong on “rubbing out” the finish then I don’t thinkl it really matters. I do know, for example, if your moving and you wrap your project before the lacquer has time to completely cure, you can end up with a somewhat “lumpy” finish.

I know this all sounds like a lot to digest and hopefully someone more experianced can give you better more precise answers. I’m just conveying my own experiences and knowledge. I prefer lacquer to poly for several reasons. Mainly, drying time because poly attracts too much dust and cat hairs. But also because lacquer doesn’t cause that “ambering affect” that poly does.

-- I have metal in my neck but wood in my blood!!

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Cosmicsniper

2199 posts in 1791 days


#9 posted 1116 days ago

Lacquer dries faster than poly, which is the main reason the pros use it. The longer the dry time, the more at risk you are to dust.

But whether there are dust nibs in poly or lacquer, I would still wipe down between coats…I don’t care if coats of lacquer do melt into each other, if dust nibs are there (which are more like dust boulders to me) you don’t want them in your lacquered finish. I use 3M sanding pads for this…the black ones for early coats and the white ones for late ones. This takes all of 30 seconds to do for typical projects…just get the nibs.

Sanding between coats of poly is only necessary to remove dust. No mechanical bond is gained by scuff sanding.

There are lots of myths to applying poly. This PWW article here does a great job of addressing them:

http://www.popularwoodworking.com/article/the_7_myths_of_polyurethane

Take note of Myth #7. That’s one of my favorites.

-- jay, www.allaboutastro.com

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BobTheFish

361 posts in 1185 days


#10 posted 1116 days ago

”MYTH #7: Scuff sand between coats to get a good bond. The purpose of this instruction is to create scratches in the surface so the next coat of finish can establish a “mechanical” bond. The finish “keys” or “locks” into the sanding scratches.

This myth is somewhat complicated. The first clue that sanding between coats isn’t so critical is that you rarely create scratches everywhere anyway. There are almost always gaps in your sanding – for example, in the pores, in recesses and often just because you aren’t being thorough enough.
And yet, the next coat usually bonds well anyway, especially if not a lot of time has gone by between coats. How often have you seen coats of polyurethane separating?”

So basically what I said I do before is perfectly fine. Especially since I go for the satiny finishes anyhow. :-/

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Cosmicsniper

2199 posts in 1791 days


#11 posted 1116 days ago

BTW, Myth #4 is one of those that I’ve always been puzzled about too. I’ve never seen a gain in drying time by thinning with naphtha.

-- jay, www.allaboutastro.com

View hObOmOnk's profile

hObOmOnk

1381 posts in 2761 days


#12 posted 1116 days ago

Note: Polyurethane is not a product; it is an ingredient.

There is no guarantee that any two polyurethane containing products are the same.
Our laboratory testing (Reed Project) shows that common consumer grade wood finishing products can vary in content of polyurethane by as much as 10 fold.

IOW, don’t assume that all “Poly” products are the same.

Likewise, chicken soup is not a chicken, it contains chicken.

Blessing,
Bro. Tenzin

-- 温故知新

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doyoulikegumwood

384 posts in 2625 days


#13 posted 1116 days ago

ok ben i will try to answer your questions on lacquer. this may get a bit long winded.

first off there are only 3 basic types of lacquer out there.

1. nitrocellulose lacquer (this is the one were talking about)

2. CAB which goes by the names CAB,CAB-acrylic, or acrylic just to confuse everyone

3. 2 part finishes which are more like a varnish lacquer highbred they come in the forms of conversion varnish,post-catalyzed lacquer, and pre-catalyzed lacquer.

ok so why wouldn’t everyone use lacquer over varnish “minwax polyurethane is varnish” well assuming we’er talking about #1 and#2 varnish is far more durable so on things that will see lots of use like a desk or table it would be preferred. thats not to say those same lacquers dont work in those situation most if not all the furniture you have grown up with was finished more then likely in lacquer.

deft brushing lacquer can be applied with a brush but a bit of warning you must work very efficiently or at the very least buy more retarding agent to slow down the drying process. I cant remember what the agent is off the top of my head but the can should let you know what it is, and its kind of like adding thinner.

so why don’t more folks out there use lacquer well first a fore most its best sprayed. brushing works fine if you work efficiently (ei once you start you cant stop and you can’t slow down)

I personally prefer lacquer it give a much better depth and is much easier to rub out. but I have been spraying for 15 years. and the only time I ever brush lacquer is for repair.

I don’t know if I answered your question or not but I hope this helped.

lol edit i was typing all of this when ceaanapilot post his lol

-- I buy tools so i can make more money,so ican buy more tools so I can work more, to make more money, so I can buy more tool, so I can work more

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hObOmOnk

1381 posts in 2761 days


#14 posted 1115 days ago

Here’s a novel and seldom used solution to this kind of problem.
Why not read the manufacturer’s instructions?.
I know, it doesn’t seem logical but give it a try. <grin>

”WARNING! Removal of old paint by sanding, scraping or other means may generate dust or fumes that contain lead. Exposure to lead dust or fumes may cause brain damage or other adverse health effects, especially in children or pregnant women. Controlling exposure to lead or other hazardous substances requires the use of proper protective equipment such as a properly fitted respirator (NIOSH approved) and proper containment and cleanup. For more information, call the National Lead Information Center at 1-800-424-LEAD (in US) or contact your local health authority.

Surface must be dry and free of wax, grease, polish, old finishes in poor condition or any foreign matter.
Sand to a smooth, uniform surface. DO NOT USE STEEL WOOL. Remove dust with a cloth dampened with water or mineral spirits. Let dry completely.
If desired, apply Minwax® Wood Finish™ or Minwax® Water Based Wood Stain to unfinished interior wood surfaces following label directions. Wait at least 24 hours before applying Polycrylic® over Minwax® Wood Finish™.
Stir well before and regularly during use. DO NOT SHAKE. FINISH APPEARS MILKY IN CAN BUT DRIES CRYSTAL CLEAR.
Apply a thin coat of Polycrylic® with a high-quality synthetic bristle brush. Apply in one direction with the grain. Do not overbrush.
Let dry at least 2 hours then sand with very fine sandpaper (220 grit) to ensure an even finish and proper adhesion of additional coats. Do not use steel wool. Remove all dust.
Apply second coat. For additional coats, repeat Step 6 before applying. Three coats are recommended.
After final coat, allow 3 hours before light handling and 24 hours before normal use.
Special Instructions: Polycrylic® should not be applied over red mahogany stain. Instead, use Minwax® Fast-Drying Polyurethane over any red mahogany stain.

Clean Up: Clean with soap and warm water immediately after use.

Coverage: Approximately 125 sq. ft. per quart

Notes: Thinning is not recommended. Keep from freezing. Store below 105°F. For interior use only. Dry times are based on good ventilation, temperature of 77°F, and 50% relative humidity. Lower temperature, higher humidity, lack of air movement or application of thick coats will extend drying times. Always test surface for tackiness between coats. Oil-based stains, paints or coatings applied under Polycrylic® may amber normally. Always spot test on an inconspicuous area to ensure satisfactory results.”

Blessings,
Bro. Tenzin

-- 温故知新

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AaronK

1397 posts in 2097 days


#15 posted 1115 days ago

hobomonk – generally a good idea, but we routinely go against a lot of these rules…. using steel wool, thinning to make a wiping varnish, using crappy foam brushed :-) etc.

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